New Associations? Schizophrenia Comorbidity

A new study in Psychiatric Services is the first systematic analysis of comorbidity in general with schizophrenia in the U.S. hospitalized population. A series of recent studies have examined single comorbidities with schizophrenia, but these studies were generally conducted with small or unrepresentative sample sizes and tested hypotheses rather than taking a broader approach. By contrast, this study looked at nearly 6 million hospital discharge records to calculate proportional morbidity ratios.

Somewhat predictably, psychiatric and behavior related diagnoses accounted for 45% of comorbidity. Anyone who has been diagnosed with schizophrenia, or has a diagnosis in their family knows that other diagnoses frequently precede or follow suit.

However, the study showed more than just that. Among non-psychiatric diagnoses, many patients with a primary diagnosis of schizophrenia were also diagnosed with acquired hypothyroidism, obesity and other hyperalimentation disorders, asthma, chronic airway obstruction not elsewhere classified, essential hypertension, and type 2 diabetes.

Head author Weber notes in a Psychiatric News article that the researchers expected cardiovascular and metabolic conditions to occur at a rate even greater than they found. Author Newcomer explained that this likely represented endemic underdiagnosis. “The very nature of the problem with this diagnosis [of schizophrenia] is that the patients tend to receive a lower standard of medical care, so there is going to be massive underestimation”.

Interestingly, the news article does not mention one likely cause of increased metabolic dysfunction among schizophrenics: weight gain, often leading to diabetes is a well-known side-effect of atypical antipsychotic use. Taking statistical comorbidity without this contextualization can be misleading, and so followup research is required. The study authors seem well aware of this, as Weber notes: “”Our study is hypothesis-generating rather than hypothesis-testing.”

Is it intuitive that psychiatric conditions would be co-morbid with non-psychiatric medical conditions? Why or why not? Do lifestyle and behavioral factors associated with mental illness increase risk? Is there is a biological connection? Finally, how much of this comorbidity is due to iatrogenic harm? If psychiatric conditions show significant non-iatrogenically induced comorbidity, what are the public health policy ramifications for the treatment of mental health?